This is a piece of equipment you'd never see, in all likelihood. But you've probably breathed dirty air from it.

It's a 1950s-era locomotive  -- technically, a "switcher locomotive" -- that SEPTA uses for maintenance, repairs and to rescue stranded trains. So it's big and it's old, which means it emits plenty of pollution.

Earlier today, the U.S. Environmental Protection Agency announced a $1.2 million grant -- through its Diesel Emissions Reduction Act Program -- to repower its engine and add a filter.

The upgrade is expected to reduce the engine's emissions of nitrous oxide and particulate matter, both of which are lung irritants, by 80 percent. It also will reduce carbon dioxide emissions by 25 percent, according to an EPA press release. And, it will use less fuel.

But don't hang around the SEPTA rail yard just yet expecting to inhale with impunity.

The engine getting the upgrade is one of six that SEPTA uses.